1. Field of the Invention
The invention concerns a lancet device which is suitable for a single use only and which is effectively unusable after a single use. The device also includes indicators by which a user can readily visibly determine whether or not the device has been used yet.
2. Description of Background information
Sharp pointed or bladed lancets are frequently used to make a small penetration of a patient's skin to let a small volume of blood for diagnostic purposes. With the growing concern over blood-transmitted communicable diseases such as AIDS, hepatitis, etc., it is becoming increasingly critical to insure that a needle or lancet, once used, is not re-used on a different patient. Thus, precautions are necessary to insure that once used, a lancet cannot be accidentally used again. Furthermore, because of the continuing threat that a used lancet poses even after disposal, it is paramount that the lancet tip be completely and securely shielded after use and disposal, to prevent accidental contact with sanitation workers or anyone else that might accidentally come into contact with the device.
Spring-energized, i.e., preloaded spring driven lancets of many types have been known and used as a replacement for needles for piercing the skin for blood samples. Some of these devices are designed as single use, disposable devices. However, the relative complexity of such devices has made them expensive to manufacture and, often, unreliable in use. For example, the preloaded spring can often lead to misfiring of the lancet tip or skewing of the spring so as to make an unacceptable incision or an incision which imparts more pain to the patient than absolutely necessary.
U.S. Pat. No. 5,356,420 discloses a preloaded device in which a puncturing tip 7 is mounted on a piston 5 within a piston sleeve 1. A power spring 9 is preloaded within the sleeve and actuated by depression of a push-button 2. An additional spring 10 is provided to ensure that the puncturing tip 7 is retracted into the sleeve after use.
Simpler disposable lancet devices which do not employ preloaded spring driving have also been devised. For example, U.S. Pat. No. 4,889,117 discloses a disposable lancet (FIGS. 7 and 8) in which a needle tip 48' is provided within a tube 50. A cap 44 is provided at one end to the tube 50. Upon depression of the cap 44, the tip 48' protrudes from the tube 50 and pierces the skin of the patient. A spring steel formed washer 60 is provided to ensure that the tip is retracted back within the tube 50 when the force is removed from the cap 44. An inwardly biased tang 62 prevents re-use of the lancet after the initial use. However, with this type of device, where a driving force implied to the cap is in the direction of the patient's skin, when the operator operates the device, the force applied for operation may apply an excessive force to the skin, which may result in unnecessary tissue damage.
U.S. Pat. Nos. 5,133,730 and 5,212,879 disclose a disposable, retractable finger stick device and method for manufacturing the same. Within a housing 12, a blade 14 is provided. A lever arm 16 protrudes from the housing 12. Upon depression of the lever arm 16, the lever arm moves a biasing member 60 to press a ramp 52 to depress a blade holder 50, thereby causing the blade 14 to protrude beyond the housing 12 and pierce the skin of the patient. The biasing member 60 locks against the ramp portion of the blade holder 50 after a single use, to thereby prevent re-use of the device. The blade and blade holder are mounted on a living hinge 48 which helps to retract the blade back within the housing after use. This device has a relatively large number of moving parts and a relatively complex arrangement, thereby increasing the cost of production.
With regard to the device disclosed in U.S. Pat. Nos. 5,133,730 and 5,212,879, as well as the device disclosed in U.S. Pat. No. 4,889,117, an operator cannot readily determine, by looking at the device, whether or not it has been used. Thus, even though an operator would not be able to accidentally stick a second patient with one of these lancets after it had already been used, a real risk still exists with the use of these devices. Because the operator cannot visually determine whether or not the lancet has been used. The possibility exists that the operator will assume that a used device has not been used. In this case, the operator will not ultimately be able to actually stick another patient. However, the operator could possible contact a second patient's skin with the housing in the location at which the blade is intended to protrude during sticking. Since in this instance, the lancet would already have been used, there is a good chance that the housing would be contaminated in this location with blood or other infectious contaminants. Thus, a real risk exists that such contaminants could be transferred to the second patient merely by contacting the housing of the used lancet device with the second patient's skin.
Thus, there is need for a simple, inexpensive, reliable, self-activating disposable lancet device which clearly indicates whether or not the device has been used.